Sur Tasna

There is appreciably less snow than usual at this time of year in most regions and snow conditions for ski touring are very poor in many places. Only in northern Lower Valais are snow depths approaching average. On southern slopes and in general below 2400 m, the snowpackSnow deposited on the ground in a multiplicity of layers.EAWS glossary has mostly frozen solid.

On the Main Alpine Ridge in Valais and in western Ticino, the small volumes of fresh snow which have fallen in the last few days are lying on a thin but weak old snowpackSnow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary of faceted crystalsSnow grains, solid, with multiple flat glassy faces and sharp edges. Developed from faceting metamorphism, usually poorly bonded to one another (fewer contact points), a critical factor in avalanches if a faceted layer is covered with bonded snow. Typical grain size: 0.5 to 3 mm See also: www.snowcrystals.itEAWS glossary. Avalanches may be triggered in these regions. In the inneralpine regions of Valais, on the southern flank of the Alps and throughout Grisons, there are sometimes pronounced weak layersSnowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary of faceted crystals or surface hoarTransparent, frequently flat crystals forming on the snowpack when moist air settles on the surface. It forms most often during cold, clear, humid nights. Once it is blanketed by fresh fallen snow, surface hoar is one of the most critical weak layer. See also: www.snowcrystals.itEAWS glossary in the snowpackSnow deposited on the ground in a multiplicity of layers.EAWS glossary, especially on northern and eastern slopes above approximately 2400 m. However, only very isolated avalanches have been triggered in these layers. Further north, the structure of the snowpack is more favourable.

Conditions were mostly overcast with high cloud. There was some light snowfall in some southern regions.

Fresh snow

A few centimetres fell locally on the Main Alpine Ridge in Valais and in Valle Maggia.

Temperature

At midday at 2000 m, between +4°C in the north and 0°C in the south

Wind

Southerly:

• moderate to strong on the northern Alpine ridge
• elsewhere light to moderate

Conditions will remain sunny in the morning but low stratus cloud cover will gather from the north in Alpine valleys up to higher than 2000 m. A little snow may fall. Over the course of the day, clouds will gather in the south and snow will start to fall. The snowfall level will be at low altitude.

Fresh snow

A few centimetres on the northern edge of the Alps and on the southern flank of the Alps

Temperature

At midday at 2000 m, between -7°C in the north and -3°C in the south

Wind

• Strong Bise wind in the north and in the Jura
• Moderate to strong southeasterly in the Alps in the afternoon

In the south, skies will be mostly overcast and snow will fall down to low altitudes. Precipitation will accumulate following a southeasterly course, especially on the Main Alpine Ridge in Upper Valais, where around 20 to 40 cm of snow will fall by Friday, with up to 20 cm falling on the rest of the southern flank of the Alps. In the north, conditions will be mostly sunny in the mountains. There will be a strong foehn wind but there is little transportable snow. Avalanche risk will increase in regions with fresh snow, significantly so on the Main Alpine Ridge in Upper Valais.